1. Field of the Invention
The present invention relates to coating processes used to produce controlled-release coatings and to products made by the process.
2. Brief Description of the Prior Art
Controlled release dosage forms are designed to provide prolonged pharmacological action after the administration of the dosage form, as compared with the administration of an immediate release dosage form. Such sustained response offers many inherent therapeutic benefits that cannot be obtained with immediate release and short acting products.
Controlled release dosage forms known in the art include coated beads, pellets or spheroids, coated capsules, coated tablets and ion exchange resins, wherein the sustained release of the active drug is realized via permeation of the active drug through a coating layer or a matrix formulation to slow down the release of the drug.
An essential characteristic of all controlled release dosage forms is the stability of the dosage forms. The stability of a pharmaceutical dosage form refers to the constancy of its physical, chemical, microbiological, therapeutic, pharmaceutical, and toxicological properties during storage in a specific container under a specific set of conditions. Stability studies are required by Good Manufacturing Practices (GMPs), the U.S.P., as well as New Drug Applications (NDAs) and Investigational New Drug Applications (INDs).
Hydrophobic polymers have been used as a film former to coat tablets, capsules, suppositories, spheroids, beads or microspheres to develop controlled release dosage forms. It is known in the prior art that these hydrophobic coatings are formulated in the form of an organic solution, pseudolatex or suspension. Since most of these polymers are insoluble in water, a polymer solution in an organic solvent is sprayed onto the individual drug forms (such as beads or tablets) and the solvent is evaporated during the coating process. However, the evaporated solvent poses environmental pollution concerns. In addition, coating formulations with organic solvents have inherent problems with regard to flammability, carcinogenicity, and safety.
For these reasons, it is desirable to use an aqueous polymer coating composition based on a latex or pseudolatex of an insoluble polymer to prepare a controlled release formulation. However the stability of coated substrates prepared using these aqueous polymer coating compositions remains a challenge. In particular, it is known that the drug release profile changes upon storage of the coated substrates. Such instability is not found when the coating is formulated by dissolution of the polymer composition in an organic solvent.